BACKGROUND AND OBJECTIVE: The aim of this study was to determine the agreement between pulmonary artery thermodilution (PA-TD) and a new pulse contour method (PCM), FloTrac/Vigileo version 1.0, and to asses the ability of FloTrac to track sudden changes in cardiac output. METHODS: Cardiac output was determined twice after induction of anaesthesia, but before cardiac surgery, with both PA-TD and a PCM in order to determine the precision of both methods. The bias and agreement between the two methods were calculated using Bland-Altman analysis. Postoperatively, in patients with heart rates under 60 beats min(-1), atrial pacing was initiated and cardiac output was determined before and after with both methods. RESULTS: Twenty-five patients were investigated. The precisions of PA-TD and the PCM were 0.35 (95% confidence interval +/-0.12) and 0.6 l min(-1) (95% confidence interval +/-0.21%). The bias between PA-TD and the PCM was -0.51 l min(-1) and the limits of agreement were +/-1.87 l min(-1) (95% confidence interval +/-0.39 and +/-0.66). The percentage error was 48%. The changes in cardiac output with atrial pacing were in the same direction in all nine patients. CONCLUSION: In this study, agreement between PA-TD and the PCM was poor, but the PCM was able to track the direction of pace-induced changes in cardiac output.